Degradation of a turbocharger may be reduced by limiting turbocharger operation to selected operating conditions. In U.S. Patent Application 2009/0090107 a model is used to estimate turbocharger speed, and a turbine actuator control law is estimated by mapping the turbine from a measurement of flow into the turbine and from a desired ratio of the pressures in the turbine. The approach then adjusts a turbine actuator to modify the turbocharger turbine geometry. The actuator modifies the flow rate to the turbine so that pressure in the intake manifold is equal to a set point pressure. However, the method appears to overlook that it may be undesirable to operate the turbocharger at a turbine expansion ratio that exceeds a turbine expansion ratio limit. Consequently, the approach may accelerate turbocharger degradation during some operating conditions.
The inventors herein have recognized engine operating conditions where it may not be desirable to operate an engine when a turbine expansion ratio exceeds a turbine expansion ratio limit. Further, the inventors have recognized that different turbine expansion ratio limits are desirable for different exhaust flow rates. For example, it may not be desirable to operate an engine to regenerate a particulate filter when regenerating the particulate filter or the method of regenerating the particulate filter can cause a turbine expansion ratio to exceed a turbine expansion ratio limit. Further, if an operator fails to change an air cleaner element, the turbine expansion ratio limit may be exceeded thereby leading to turbocharger degradation. However, it may be desirable to permit a higher turbine expansion ratio limit at low engine speeds when exhaust flow rates are lower and turbocharger degradation is less likely so that the driver may have an expected level of engine performance or particulate filter regeneration function.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: operating an engine with a turbocharger; adjusting operation of the engine in response to a turbine expansion ratio exceeding a turbine expansion ratio limit of the turbocharger, the turbine expansion ratio limit varying in response to an exhaust gas flow rate.
By adjusting operation of an engine in response to a turbine expansion ratio limit, engine operation can be limited such that the possibility of turbocharger degradation may be limited. For example, if a particulate filter is scheduled to regenerate a higher altitude the particulate filter regeneration can be delayed until then engine is at a lower altitude or different operating mode when regeneration can be enabled. Further, if during normal engine operation the turbine expansion ratio exceeds a desired expansion ratio limit, the engine output or other operating parameters can be reduced so as to reduce the possibility of operating the turbocharger turbine at an expansion ratio that exceeds a turbine expansion ratio limit.
The present description may provide several advantages. For example, the approach may reduce the possibility of turbocharger degradation. Further, the approach may provide an improved basis for turbine expansion ratio limits. Further still, the approach may be beneficial for improving a variety of engine operating conditions including particulate filter regeneration and engine operation with reduced intake system capacity.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.